Development of lightweight, small, and electrically efficient antennas and antenna systems continues to increase with an ever greater need to transmit large amounts of data. Research into ultra-wide band systems is hoped to further address this need. Small size and lightweight construction are paramount in the development of future systems so that the antenna can be contained in a wearable, easily transportable, or lightweight system. Typically small size is defined as having a dimension of λ/10 or less. In addition, future antenna systems should cover a frequency range from 20 MHz to 6 GHz or broad ranges therein so as to be applicable to many systems ranging from the traditional HF and UHF bands as well as for use in the ever more heavily used wireless computer network and cellular bands of 3-5 GHz.
Many prior systems attempting to have wide band applicability employed combinations of antenna shapes. However, these suffer from the need for significant feed networks that add to the cost, complexity and weight of the system. Other attempts used combinations of monopoles of varying height, but these require a stepped sequence for both transmitting and receiving data.
In the very- and ultra-high frequency (VHF/UHF) and microwave frequency range, previous efforts to broaden the impedance bandwidth of a conventional quarter-wavelength wire monopole primarily involved sleeve monopoles or loading the wire with lumped elements. The sleeve monopole uses multiple additional wire radiators of shorter length surrounding the central main radiator to create an additional resonance, resulting in a broadened impedance bandwidth. Of concern, however, is the larger physical footprint of the antenna system, which is especially troubling at low frequencies. The weight of the antenna system also increases due to the added thick copper wires. The other technique employs strategically placed serial lumped LR (inductive and resistive) circuits along the monopole to introduce multiple resonances and thus a broader impedance bandwidth. Several physical and performance related drawbacks arise with this technique as well. Mainly, the length of the monopole is greatly elongated, the weight is increased due to the added loading and matching network, and the gain is reduced due to the losses of the circuit elements. Moreover, the cost is increased due to the addition of the RL circuit elements.
As such, there is a need for a wide-bandwidth antenna that does not significantly increase antenna complexity, footprint, or weight.